#include <iostream>
using namespace std;
const double PI = 3.14;
class cir{
    //公共权限
public:
    //属性
    double m_r;
    //行为
    void zc(){
        cout<<"圆的周长是："<<2*PI*m_r<<endl;
    }
};
int main()
{
    //创建类对象
    cir c1;
    c1.m_r=5.4;
    c1.zc();
    return 0;
}